ATLANTA — A small explosion and power outage at a concourse of Atlanta's Hartsfield-Jackson International Airport was likely caused by a malfunctioning power supply unit Tuesday morning, airport officials said.

Passengers were allowed to return to their gates at the airport after an electrical explosion at a maintenance shop knocked out some power to one of the concourses, authorities said. No one was injured.

The explosion happened around 8:40 a.m. at a maintenance shop near Gate D 21, said airport spokesman Reese McCranie.